Influenza is not likely to cause relapse of multiple sclerosis (MS)
in adults, according to an Institute of Medicine (IOM) report.

The Immunization Safety Review Committee of the IOM reviewed data on
influenza vaccine and neurological conditions. They note in their report
entitled "Influenza Vaccines and Neurological Complications" that evidence
of any linkage is complicated by continuing antigenic changes in influenza
viruses, necessitating yearly reformulation.

The Centers for Disease Control and Prevention recommends a flu shot
for individuals 6 months or older who are at increased risk of influenza
complications, for all individuals ages 50 to 64, and for healthcare workers
who can transmit infections to high-risk individuals.

After an extensive review of primarily published, peer-reviewed scientific
and medical literature, IOM committee chair Dr. Marie C. McCormick, of
Harvard School of Public Health in Boston, and colleagues concluded that
the "evidence favors rejection of a causal relationship between influenza
vaccines and relapse of multiple sclerosis in adults."

Because of the paucity of studies examining the link between vaccine
and onset of MS, the IOM committee concludes that the evidence is inadequate
to reject a link between the vaccines and incident MS in adults, but "sees
no reason to suspect that a causal relationship might exist."

However, the committee notes that there is consistent, strong evidence
of a causal link between the 1976 influenza vaccine, used to prevent a
"swine flu" epidemic, and Guillain-Barr syndrome (GBS). Otherwise, the
group says, evidence is inadequate to accept or reject a causal relationship
between GBS in adults and modern influenza vaccines.

Moreover, evidence is inadequate to address the relationship between
influenza vaccines and optic neuritis or other demyelinating neurological
disorders. Furthermore, there are no published studies that directly address
vaccines in children, especially those between 6 and 23 months old.

In evaluating the public health significance of their report, the authors
point out that there is a substantial burden of morbidity and mortality
associated with influenza infections, and that "the prospect of an influenza
pandemic is a serious concern to many." The vaccine is 70% to 90% effective
in preventing illness among individuals between 6 months and 65 years old.

Although less effective in preventing illness in older and more frail
individuals (30% to 40%), the vaccine is 50% to 60% effective in preventing
hospitalization and 80% effective in preventing death in this age group.

Overall, any risk of neurological complications directly attributable
to influenza vaccine, which is small at most, must be "appropriately weighted
against the sizable burden of illness associated with influenza infections."